Is the island of cuba is substantially larger than the island of jamaica?

Yes, Cuba is much bigger than Jamaica. The territory of Cuba is 109,884 square kilometers while the territory of Jamaica is 10,990 square kilometres, which means that Cuba is pretty much 10 times bigger in territory than Jamaica. It might be a bit confusing if you don't know the exact territories because Cuba ranks as the biggest island in the Caribbean and Jamaica ranks as the fourth biggest, so you would assume that their territories are closer in size especially because they are both islands.

the only other powers were germany russia and uk and they were too busy fighting each other wearing each other down   that the us was becoming strong and they were becoming weaker

the answer is the last option or letter d)